This invention concerns arthroplasty, and, more particularly, resides in improved cutting guides having features to better assist a surgeon in preparing a bone, for example, to receive an implant.
Whether for primary or revision arthroplasty, cutting guides are typically employed to ensure that any required resections correspond to mating surfaces of the prosthetic component. In knee replacement surgery, for example, a rod is typically inserted into the medullary canal of the proximal tibia, and a cutting guide is temporarily secured to this rod. Such guides include one or more slots into which the blade of an oscillating saw is inserted from anterior to posterior to shape the end of the bone in accordance with corresponding surfaces of the prosthetic element.
Extramedullary guide systems are also familiar to the art and typically provide a means for alignment and securing a cutting block on the proximal tibia.
In the case of a revision, the procedure is usually more elaborate due to deterioration of the previously prepared surfaces resulting from decomposition of the bone/prosthesis interface, necrosis, osteolysis, and other factors. Cutting blocks used in revision procedures therefore include slots corresponding to augments used to fill gaps between major resections and the mating surfaces of the prosthetic component. In the case of proximal tibial repair, such augments are typically wedge-shaped to account for proximal loss. Although more recently introduced techniques attempt to base the cuts on an intramedullary guide to which additional cutting blocks are mounted, there remains an unacceptable margin of error, the correction of which in some cases requires a freehand shaping of the bone. In addition, lateral defects require reshaping without injury to the patellar tendon which obstructs a saw blade when approached from the front of the knee.
The present invention accordingly provides improved cutting guides which enable one performing a resection to better predict and execute required cut characteristics. Broadly, and in general terms, the invention comprises a body having an outer surface and an inner surface configured to be positioned against a bone surface to be modified. Preferably, the inner surface is substantially flat to mate with a previously executed planar resection. The body further includes one or more openings extending therethrough, from the outer to the inner surface, enabling a bone-cutting tool to be used though the body so as to perform resections below the inner surface. To stabilize the bone-cutting tool during the execution of a particular resection, the invention preferably further includes one or more guides which may be temporarily positioned relative to the upper surface with which the cutting tool physically interacts to perform an accurate cut.
One application of the invention is therefore in proximal tibial preparation as part of a partial or total knee replacement, whether as part of a primary or revision procedure. In this embodiment, the body may be plate-shaped, and affixed to the proximal tibia using an intramedullary stem, or screws, pins or other fastening mechanism appropriate under the circumstances. The openings through the plate may include one or more slots to receive a bone-cutting saw or, alternatively, may take the form of apertures having side surfaces against which a bone-cutting tool or saw may be positioned during resection. The guides in this case are provided in the form of blocks, each having a first surface adapted for positioning against the outer surface of the body, and a second surface used to stabilize the movement of the cutting tool.
In a preferred implementation of the embodiment of the invention used for proximal tibial resection, the body may take the form of a tray of the type used as a sizing plate or final implant, which includes an outer, peripheral lip configured to receive an articular surface insert, which is typically constructed of polyethylene. In this case, the invention may include an insert with a shape corresponding to the final insert, and may be constructed of metal, polymeric or other suitable material, but with slots or other openings which function as cutting guides. As such, the invention may also be used for trialing purposes by reducing the tray and insert with guides into a joint situation and, upon a successful trial reduction, once again exposed and subsequently used as a cutting guide, with confidence that the final implant will fit properly, including any required augments.